This invention relates to methods for dressing grinding wheels and, more particularly, relates to dresser tools of abrasive compacts.
Dressing may be defined as any operation performed on the face of a grinding wheel that improves its cutting action. Trueing is a dressing operation but is more precise, i.e., the face of the wheel may be made parallel to the spindle or made into a radius or special shape. Regularly applied trueing is also needed for the accurate size control of the work, particularly in automatic grinding.
Opening is another dressing operation and refers to the breaking away of the bond material from around the abrasive particles in a wheel thereby exposing them for grinding. A new wheel is initially opened and may have to be periodically opened thereafter to expose new particles when the previously exposed particles have been dislodged or dulled and to remove grinding swarf, which may accumulate during grinding, from around the abrasive particles.
Reference can be made to Machinery's Handbook (20th Ed. 1976) pp. 1992 to 1994 for a listing of commonly used dressing tools and methods for their use. One common type is a single point diamond tool having a granular shaped diamond mounted at one end of a tool shank. Dressing is performed with such a tool by engaging the periphery of a rotating wheel with the cylindrical handle of the tool disposed at a negative angle of 10.degree. to 15.degree. relative to a line drawn perpendicular to a tangent to the wheel periphery at the point of engagement of the tool with the wheel. This is equivalent to a negative back rake angle of about 55.degree. to 60.degree.. The tool is also occasionally rotated about its longitudinal axis to prolong diamond life by limiting the extent of the wear facets and also to produce a pyramidal shape of the diamond tip.
It is also common to use a dresser having a plurality of individual diamond mounted in an array, e.g., straight line, across the nib of the dresser. These dressers are generally referred to as multi-point or cluster type. In use, the dresser is canted at an angle of 3.degree. to 10.degree., bringing two to five individual diamond points into contact with the grinding wheel. The multiple points often permit faster cross feed rates than the single point dresser.
Another method of dressing is disclosed in the above mention application of Dennis and Skinner, Ser. No. 906,288 wherein a compact abrasive dresser is disposed at a positive rake angle to the grinding wheel.
Still another type of dresser is disclosed in our above-identified application, wherein a plurality of cluster compacts or composite compacts are utilized to dress abrasive wheels.
While the prior dresser tools are generally considered to be satisfactory, manufacturers are always concerned with improving the grinding process, such as by improving the wheel life, wheel cutting speed, surface finish on the workpiece produced by the grinding wheel, dressing tool life and dressing speeds.
Present dressing techniques "glaze" the grinding wheel slightly to produce a smooth surface finish. This produces a poor cutting wheel that "burns" the object during grinding. It is desirable that the grinding wheel be both "free cutting" and capable of producing a smooth surface finish. "Free cutting" refers to a grinding wheel's capability of rapidly removing material from a workpiece and requiring low cutting energy input from the grinding machine. But the present technology, has not been able to meet the two fold criteria of free cutting and smooth surface finish because of the trade off inherent in the present dresser tools.
Accordingly, it is a feature of this invention to provide a dressing action which enhances and improves the grinding process in these areas.
Another feature of this invention is to provide an improved dressing tool particularly applicable for dressing grinding wheels which will grind workpieces and improve both free cutting and smooth surface finish characteristics.